Sometimes Google AdWords will not verify third party tracking numbers because their bots cannot see the number when they crawl the site. In order to bypass this, you’ll need to link your AdWords account to the Search Console inside of AdWords. Having these two accounts linked bypasses the need for the bots to crawl your site.
If you do not have both AdWords and the Search Console linked, Google is going to need to verify the ownership of the number by going to your website and comparing numbers. If your numbers do not match (which they likely will not if you are using CallTrackingMetrics), they will not approve the ad.
We recommend having separate numbers for Google AdWords and ad extensions, and we also recommend having a designated number for your call-only ads. This will create flawless and easily manageable reporting.
For more information about Google’s phone number verifying process, see their support page here.